The present invention relates to the construction of reinforced soil structures. This building technique is commonly used to produce structures such as retaining walls, bridge abutments, etc.
A reinforced soil structure combines a compacted fill, a facing and reinforcements usually connected to the facing.
Various types of reinforcement can be used: metal (for example galvanized steel), synthetic (for example based on polyester fibers), etc. They are placed in the earth with a density that is dependent on the stresses that might be exerted on the structure, the thrust of the soil being reacted by the friction between the earth and the reinforcements.
The facing is usually made from prefabricated concrete elements, in the form of panels or blocks, juxtaposed to cover the front face of the structure.
There may be horizontal steps on this front face between various levels of the facing, when the structure incorporates one or more terraces. In certain structures, the facing may be built in situ by pouring concrete or a special cement.
The reinforcements placed in the fill are secured to the facing by mechanical connecting members that may take various forms. Once the structure is completed, the reinforcements distributed through the fill transmit high loads, that may range up to several tons. Their connection to the facing needs therefore to be robust in order to maintain the cohesion of the whole.
These connections between the reinforcements entail a risk that the maximum load they can withstand may be exceeded if the soil undergoes strong differential settlement or in the event of an earthquake. Furthermore, the connecting members exhibit risks of degradation. They are more susceptible to chemically degrade, for example by corrosion for steel or by hydrolysis for polyester based connections, due to moisture or chemical agents present in or which have infiltrated into the fill and concentrate in the vicinity of the facing.
Reinforced soil structures are designed for a certain duration of use. For example, road and railroad structures are expected by the owners to be in service for periods exceeding 75 years, or exceeding 100 years. If the structures are properly designed and built, they will maintain their required safety level for those periods of time. But after, the level of safety will decrease slowly up to reaching a level at which the tension applied on a reinforcement or a series of reinforcements is higher than the residual strength. If this has not been anticipated, a failure of the structure will happen. The experience shows that this failure is likely to happen at or at the vicinity of the connection points onto the facing elements. A part of the facing elements is then possibly falling down and the immediate consequence is a loss of fill which is no longer restrained. This can lead to a rapid loss of service of the structure, in particular an impossibility to maintain the use of the assets located on top of the reinforced fill structure, like roads, railways, storage facilities, . . . .
If design or construction is defective, or if the condition of the structure evolves in an unfavorable way during the service period of the structure (for example external pollution of the fill with aggressive agents), the same phenomenon can happen at an earlier stage, before the end of the expected service period.